EXTENDED SECTION: THE SCIENCE OF ANCIENT DNA — HOW RESEARCHERS READ THE PAST FROM BONE

One of the most remarkable things about the Kennewick story — and one that rarely receives adequate explanation in popular coverage — is the sheer technical achievement of extracting usable genetic information from bone that had been buried in wet riverbank sediment for eight thousand years.

DNA is a fragile molecule.

In a living organism, it is constantly being repaired by enzymatic machinery that reads the genetic code, finds errors, and corrects them.

In death, this repair machinery stops.

The DNA begins to degrade.

Over years and decades and centuries, the long chains of nucleotides — the chemical letters that spell out the genetic code — break into shorter and shorter fragments.

Chemical damage accumulates.

Contaminating DNA from bacteria, fungi, and the hands and breath and skin of researchers who handle the bones layers itself over the original genetic signal.

By the time remains are thousands of years old, the DNA that remains is fragmentary, damaged, and contaminated.